In conventional machine tools, such as lathes, drill presses, milling machines, cutters, grinders, gear forming or inspection equipment, etc., a workpiece or tool must be gripped securely and rotated precisely in alignment with a turning axis of the machine tool. For a workpiece or tool with a bore or center hole of a given inside diameter, an arbor assembly typically has a collet as an outward expansion element which is pressed radially outwardly against the internal sides of the bore or center hole by the inclined faces of an arbor body movable axially relative to the expansion element. For a workpiece or tool with a body portion or shaft of a given outside diameter, a chuck assembly typically has a collet as an inward expansion element which is pressed radially inwardly against the external sides of the body portion or shaft by the inclined faces of a chuck body movable relative thereto.
A desired objective for such arbor or chuck assemblies is to be able to expand and release the expansion element to hold a given inside or outside diameter uniformly and with a minimum of offset or distortion, such that the workpiece or tool is repeatedly gripped by the expansion pressure as precisely evenly as possible and rotated with its center axis in precise alignment with the machine tool axis. In conventional assemblies, the arbor or chuck bodies have linear portions which slide along corresponding linear portions of the collet for relative axial movement. The metal-to-metal contact between the linear portions of the movable parts typically has a clearance of from 0.0005 to 0.002 inch. The metal-to-metal contact can also produce sticking, imbalances, or uneven side loads. For high precision work, displacement of the axial position of the workpiece or tool between chucking and unchucking by as little as 0.0005 to 0.002 inch can result in unsatisfactory performance. It is therefore deemed desirable to obtain high precision tolerances of at least an order of magnitude lower or more than such conventional tolerances.
Therefore, it is a principal object of the invention to provide an arbor or chuck assembly which holds a given inside or outside diameter by a movable expansion or contraction member uniformly and with a minimum of distortion. Specifically, it is desired to provide such an assembly in which the arbor or chuck body moves in contact with the movable member with substantially zero clearance and in a substantially frictionless and distortion-free manner.